1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image with use of a developer.
2. Description of the Related Art
Image forming apparatus that use a developer including toner form an image, for example, in the following manner. That is, first, an electrostatic latent image is formed on a photosensitive drum serving as an image carrier, and the latent image is developed by a developer unit. Then, the toner image thus obtained is transferred onto a sheet by a transfer portion, and the image is fixed onto the sheet by the fuser.
Of the image forming apparatus, a type which removes toner remaining on the photosensitive drum after transfer of a toner image onto a sheet by a cleaning unit, and recycles collected toner, which is to be called recycle toner hereinafter, is conventionally known.
In connection with the above, for example, a toner recycle mechanism is conventionally known. With this mechanism, recycle toner is returned directly into a developer unit as the recycle toner carried by the collecting mixer provided in the cleaning unit is conveyed by the coupling mixer provided between the cleaning unit and the developer unit.
With the above-described structure, the collected recycle toner is being supplied to the developer unit whenever the collecting mixer and coupling mixer are rotated.
The recycle toner to be re-used contains toner particles from which a unique external additive is partially peeled off, or toner particles to which an external additive peeled off from other particles are attached, or paper dust mixed thereinto. Therefore, as compared to fresh toner whose amount of the external additive is appropriately set, the recycle toner exhibits a slow rising in amount of charge. Further, in case where charging by friction (triboelectrification) caused by stirring is not sufficient, it is possible that the recycle toner is supplied to the photosensitive drummer without being charged at all.
Uncharged toner, when transferred onto a sheet via a photosensitive drum, cause drawbacks such as creating fog in image and scattering of the toner.